Field of the Invention
The invention relates to a device and a method for the heating of a catalytic converter for an internal combustion engine, which is equipped with electrically assisted exhaust gas turbocharging.
The pollutant emission of an internal combustion engine can be effectively reduced through catalytic after-treatment using a catalytic converter. An important prerequisite for this, however, is that the catalytic converter has reached its operating temperature. Various warm-up strategies are known for ensuring rapid attainment of the so-called light-off temperature while nevertheless reducing the emission of pollutants during the cold starting phase of the internal combustion engine, in which approximately 70 to 90% of the total HC and CO pollutants are emitted during the first 10-15 seconds.
A very effective method that is frequently employed for heating the catalytic converter during cold starting is the admission of high-oxygen containing secondary air (ambient air) upstream of the catalytic converter, which when given a simultaneously high proportion of unburned fuel in the exhaust gas leads to rapid heating of the catalytic converter due to afterburning of the fuel. For the injection of the secondary air into the exhaust line upstream of the catalytic converter, however, it is necessary to produce a pressure gradient, since the exhaust gas pressure generally exceeds the ambient pressure.
The build-up of excess pressure in relation to the exhaust gas pressure is generally achieved by a separate secondary air pump. Published, European Patent Application EP 0 469 170 A1 discloses a method for the heating of the catalytic converter for an internal combustion engine, in which secondary air is injected downstream of the exhaust valves by a separate secondary air pump. An electrically actuatable pump, such as a vane pump, the delivery of which is adjustable, here serves as the secondary air pump. The delivery is pilot-controlled as a function of operating parameters of the internal combustion engine and with active lambda control according to a probe signal of a lambda probe the pilot control is corrected by an override control.
A further known method of increasing the volumetric efficiency and thereby boosting the power output of the internal combustion engine is to provide an exhaust-gas turbocharger, the turbine of which is disposed in the exhaust line and is mechanically connected by way of a shaft to a compressor disposed in the intake line. The exhaust gases from the internal combustion engine consequently drive the turbine and this in turn drives the compressor. The compressor delivers a pre-compressed fresh charge to the internal combustion engine. An air intercooler connected to the compressor on the outlet side dissipates compression heat via a coolant circuit of the internal combustion engine. The volumetric efficiency can thereby be further improved.
In order to avoid the disadvantages of the conventional turbocharger system, especially the relatively low torque at low speeds and the so-called xe2x80x9cturbo lagxe2x80x9d, an electrically assisted exhaust-gas turbocharger systems have been proposed (see the references by Zellbeck, Hans; Friedrich, Jxc3xcrgen; and Berger, Carsten: titled xe2x80x9cDie elektrisch unterstxc3xctzte Abgasturboaufladung als neues Aufladekonzeptxe2x80x9d [The Electrically Assisted Exhaust Gas Turbocharger for a New Charging Concept], MTZ Motortechnische Zeitschrift 60 (1999), 6, pages 386-391, and by S. M. Shahed et al: titled xe2x80x9cElektrisch unterstxc3xctzte Turboladersysteme fxc3xcr konventionelle Hybrid- und Brennstoffzellenantriebexe2x80x9d [Electrically Assisted Turbo Charged System for Conventional Hybrid and Fuel Cell Engines], 21st International Viennese Motor Symposium, May 4-5 2000, Series 12, Verkehrstechnik/Fahrzeugtechnik No. 420, Vol. 1, p. 310-324).
In this case, in order to assist the exhaust-gas turbocharger either an electric motor is fitted on the shaft of the turbocharger that connects the turbine to the compressor, or an electrically driven centrifugal compressor is provided, which as additional air source is connected in series to the compressor of the exhaust-gas turbocharger.
It is accordingly an object of the invention to provide a device and a method for the heating of a catalytic converter for a supercharged internal combustion engine which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, by which secondary air injection can occur.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for heating a catalytic converter disposed in an exhaust line of a supercharged internal combustion engine. The device contains an exhaust-gas turbocharger having a compressor disposed in an intake line of the supercharged internal combustion engine and a turbine with a shaft connected to and driving the compressor. The turbine is disposed in the exhaust line of the supercharged internal combustion engine. An electrically driven compressor is disposed, upstream of the compressor of the exhaust-gas turbocharger, in the intake line of the supercharged internal combustion engine. A branch is connected to the intake line downstream of the electrically driven compressor and through the branch at least a proportion of air compressed by the electrically driven compressor can be diverted. The branch is connected to the exhaust line upstream of the catalytic converter of the supercharged internal combustion engine, so that with the electrically driven compressor switched on secondary air is introduced into the exhaust line as required.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a device for heating a catalytic converter disposed in an exhaust line of a supercharged internal combustion engine. The device contains an exhaust-gas turbocharger having a compressor disposed in an intake line of the internal combustion engine and a turbine with a shaft connected to and driving the compressor. The turbine is disposed in the exhaust line of the supercharged internal combustion engine. An electric motor is disposed on the shaft and additionally drives the compressor of the exhaust-gas turbocharger independently of the turbine of the exhaust-gas turbocharger in certain operating ranges of the supercharged internal combustion engine. A branch is connected to the intake tract downstream of the compressor, and through the branch at least a proportion of air compressed by the compressor can be diverted. The branch is connected to the exhaust line upstream of the catalytic converter of the supercharged internal combustion engine, so that with the compressor switched on secondary air is introduced into the exhaust line as required.
The invention is characterized in that in a two-stage concept for supercharging internal combustion engines, in which the first stage is performed by a conventional exhaust-gas turbocharger containing the turbine and the compressor, and the second stage by the electrically driven compressor. The electrically driven compressor is also used to provide the secondary air used for the heating of the catalytic converter.
The pressure gradient produced by the electrically driven compressor permits a secondary air injection into the exhaust line without the need for a separate secondary air pump. In addition to a reduction in the cost of the overall system, this also results in a compact configuration of the exhaust after-treatment system.
In accordance with an added feature of the invention, an electrically actuatable shutoff valve is inserted in the branch.
In accordance with an additional feature of the invention, the branch opens into the exhaust line at a point close to exhaust valves of the supercharged internal combustion engine.
In accordance with a further feature of the invention, the branch opens into the exhaust line at a point downstream of the turbine of the exhaust-gas turbocharger.
In accordance with another feature of the invention, a multi-way valve with connected branch lines is inserted in the branch downstream of the electrically actuatable shutoff valve. By use of the multi-way valve, the secondary air can either be introduced into the exhaust line at a point close to exhaust valves of the supercharged internal combustion engine, or into the exhaust line at a point downstream of the turbine of the exhaust-gas turbocharger, or simultaneously at both points.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for heating a catalytic converter disposed in an exhaust line of a supercharged internal combustion engine having an exhaust-gas turbocharger with a compressor disposed in an intake line of the internal combustion engine and driven by a shaft of a turbine disposed in the exhaust line of the supercharged internal combustion engine. The method includes disposing a further electrically driven compressor, serving to assist the exhaust-gas turbocharger, upstream of the compressor in the intake line of the internal combustion engine; and feeding at least a proportion of air compressed by the electrically driven compressor, as required, as secondary air into the exhaust line of the internal combustion engine upstream of the catalytic converter by way of a branch.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, a method for heating a catalytic converter disposed in an exhaust line of a supercharged internal combustion engine having an exhaust-gas turbocharger with a compressor disposed in an intake line of the internal combustion engine and driven by a shaft of a turbine disposed in the exhaust line of the supercharged internal combustion engine. The method includes disposing an electric motor on the shaft for additionally driving the compressor of the exhaust-gas turbocharger independently of the turbine of the exhaust-gas turbocharger in certain operating ranges of the supercharged internal combustion engine; and feeding at least a proportion of air compressed by the compressor, as required, as secondary air into the exhaust line of the supercharged internal combustion engine upstream of the catalytic converter by way of a branch.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and a method for the heating of a catalytic converter for a supercharged internal combustion engine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.